Purpose: :
We are examining the structural features of melanosomes, lysosomes and lipofuscin in the retinal pigment epithelium (RPE) of monkeys and mice in order to understand how these cytoplasmic structures develop and change with age and pathology.

Methods: :
Electron microscopy is used to examine the RPE of rhesus monkeys and pigmented and albino mice. We also examined abcr -/- mice, in which lipofuscin accumulation is excessive. The mice studied are 1-2 and the monkeys 1 to 35 year of age. The life span of mice is about 2 years and for monkeys in captivity about 35-40 years.

Results: :
Melano-lysosomes containing lipofuscin are not found in 1 year old but are in 6 year old monkeys and increase in number with age, especially in the macular area. In mice melano-lysosomes are present at 1 and 2 years of age. Monkey melano-lysosomes tend to be quasi-circular structures with a homogeneous matrix containing melanosomes and lipofuscin. In mice melano-lysosomes tend to be more pleomorphic and contain less melanosomes making them similar in pigmented and albino mice.

Conclusions: :
Melanolysosomes with lipofuscin appear earlier in the RPE of mice than monkeys and monkeys accumulate melano-lysosomes earlier in life than humans (Gouras et al, Exper Eye Res 2011). If we assume that the turnover of outer segments occurs at a similar rate in monkeys and man and probably also in mice, than there must be another factor in addition to the large phagosomal load presented to the aging RPE that causes the buildup of these cytoplasmic structures. This other factor appears to be related to life span. The life-span dependent factor could be the ability of the organism to counteract oxidative stress. This same life span factor may also be responsible for the difference in appearance of melano-lysosomes in monkeys versus mice.